A Study On The Liquid-Phase Exfoliation Of Few Layer Bisumth Iodide Nanosheets

Due to their unique properties,bismuth iodide(Bi I₃)nanosheets are widely applied in many fields,such as detectors,sensors,capacitor and photovoltaic materials.Among these methods for the preparation of bismuth iodide nanosheets,the liquid phase exfoliation method is considered to be one of the most effective methods for the mass production ofbismuth iodide nanosheets.However,the study on the liquid phase exfoliation of Bi I₃ is very scarce and the used solvents are toxic.In addition,the layers number of the nanosheets is unable to control.Hence,the development of a low-cost,high-yield,controlled-layer and green liquid-phase exfoliation method for the preparation of bismuth iodide nanosheets is still a challenge.In view of the current problems,the liquid phase exfoliation of bismuth iodide nanosheets in salt-triacetin green mixed solvents and the liquid exfoliation method based on the bismuth iodide intercalated by ammonia are developed to obtain Bi I₃ nanosheets with high-quality and high-yield.The main research contents are as follows:1.The Bi I₃ nanosheets are prepared by liquid phase exfoliation method intriacetin with the aid of sodium fluorosilicate,potassium fluorosilicate,ammonium fluorosilicate,sodium citrate,sodium tartrate or ethylenediaminetetraacetic acid disodium salt as intercalate agents.The results show that the dispersion concentration and yield of Bi I₃ nanosheets in triacetin are obviously enhanced by the addition of salts.The Bi I₃ nanosheets prepared in all systems own high purity and integrated crystal structure.In addition,the thickness of bismuth iodide is mainly about 0.8 to1.4nm,which belongs to two-layer Bi I₃ nanosheets.The mechanism investigation indicates that the p Ka of the anion and the size of the cation in salts play an essential role in the dispersion concentration and the yield of Bi I₃ nanosheets.2.Three green ester mixed solvents(including methyl salicylate/triacetin,methyl salicylate/diethyl phthalate,and methyl salicylate/ethyl benzoate)are used in the liquid phase exfoliation of Bi I₃ as medium.It is found that the yield of Bi I₃ nanosheet is as high as about 30%(relative to the starting Bi I₃)and this dispersion content is 1.56mg/m L in methyl salicylate+triacetin mixed solvent with methyl salicylate volume fraction of 0.8.The thickness of Bi I₃nanosheets is in the range from 5 to 10 nm and the lateral dimension is around 1?m,The Bi I₃nanosheets still remain single crystals structure with high quality.The mechanism study suggests that the solvent-cosolvent interactions(heteroassociation)are a critical factor in the liquid-phase exfoliation of Bi I₃ nanosheets in binary mixed solvents.In addition,the as-prepared few-layer Bi I₃nanosheets have been used as catalyst to improve the C-C cross-coupling reaction between phenyl boronic acid and aryl iodides.Compared to the bulk Bi I₃,the yields of the products catalyzed by Bi I₃nanosheets were doubled,and the reaction time was shortened by one third.The catalytic activity of Bi I₃nanosheets could be maintained after 9 cycles.3.A new liquid phase exfoliation method based on the ammonia intercalation is developed to prepare the single layer Bi I₃ nanosheets.It is found that the yield of Bi I₃ nanosheets is more than27%and the dispersion content is 1.38mg/m L.The thickness of as prepared Bi I₃ nanosheets is in the range from 1 to 2 nm,and the lateral dimension is about 80-100nm.Furthermore,the Bi I₃nanosheets still remain crystals structure with high quality.The mechanism study indicates that Bi I₃can form intercalation compound with ammonia.The ordered insertion of ammonia among Bi I₃ layers makes the distance between the layers longer and weakens van der force among layers,resulting in the easy exfoliation of Bi I₃and the increase in the layers uniformity of Bi I₃nanosheets.